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F Dautry

Publications and source records attributed to F Dautry.

At least 37 records · Page 2Linked to original sources
PubMed1995

Regulation of pre-mRNA processing by src.

BACKGROUND: Changes in gene expression in response to external signals provide a key mechanisms for the regulation of higher eukaryotic cell functions. The importance of transcriptional control in the response of cells to growth factors and cytokines has been extensively documented, but gene expression has also been shown to be controlled at other levels, such as the stability of mRNA in the cytoplasm, its localization and translation. By contrast to transcriptional control, little is known of the contribution of pre-mRNA nuclear processing to the regulation of gene expression, as most of our knowledge of pre-mRNA processing in vivo is indirect, being inferred from comparisons of transcription rates and levels of mRNA accumulation. RESULTS: In this study, we have used as a model the well-characterized maturation pathway of transcripts of the cytokine, tumour necrosis factor beta (TNF beta). We have used the murine TNF beta gene as a reporter for pre-mRNA processing, using a co-transfection approach to investigate whether overproduction of proteins involved in signal transduction influences the processing of TNF beta transcripts. Although transfection of both activated ras and src genes led to an increase in RNA accumulation in the nuclear and cytoplasmic compartments, as expected from their transactivation of the TNF beta expression vector, only src induced a modification of RNA processing. Comparison of several modes of src activation indicated that two distinct effects of src on pre-mRNA processing can be coupled: one involves slowing down splicing and the other allows the export of partially spliced transcripts. These effects can be observed not only on the three introns of TNF beta but also on transcripts from a beta globin expression vector. DISCUSSION: We have characterized how the processing of transcripts of TNF beta and beta globin is regulated by the signal transduction pathway that includes the Src protein, establishing that external signals have the capacity to regulate gene expression at a post-transcriptional level within the nucleus. Src seems to act on a general mechanism of splicing and/or mRNA transport, but its biologically relevant targets are likely to be restricted to genes for which either alternative processing pathways are in competition, or the kinetics of splicing is critical. This regulation could reflect a modulation by Src of the activity of components of the splicing and transport machineries, but could also involve RNA-binding proteins, which have been shown to interact with Src.

3T3 Cells↗
PubMed1994

In vitro inhibition of the pim-1 protooncogene by chimeric oligodeoxyribonucleotides composed of alpha- and beta-anomeric fragments.

We show that oligodeoxyribonucleotides (oligos) composed of alpha- and beta-anomeric sections can be used as antisense compounds. An octamer has been chosen as an effector domain to form a substrate for RNaseH. This octamer is complementary to the translation start site of the pim-1 protooncogene mRNA. Chimeric alpha-beta oligos and their beta-analogs have a similar binding affinity for their target. These oligos also direct efficient RNaseH-mediated cleavage of target mRNA. Among all alpha-beta oligos studied, one with an alpha-fragment bound by its 3'-end to the 3'-end of the beta-octamer is the most resistant to nucleolytic digestion in biological media. The alpha-beta oligos have been found to inhibit in vitro translation of pim-1 RNA with specificity.

Animals↗
PubMed1994

Nucleic acid binding and intracellular localization of unr, a protein with five cold shock domains.

The unr gene was identified as a transcription unit located immediately upstream of N-ras in the genome of several mammalian species. While this genetic organization could be important for the transcriptional regulation of unr and N-ras, the function of the protein product of unr is unknown. unr is ubiquitously expressed and codes for an 85 kDa protein which is not closely related to previously characterized proteins. Nevertheless, a search for protein motifs has indicated the presence of five 'cold shock domains' within unr, a motif present in procaryotic cold shock proteins and in the vertebrate Y box factors. As these proteins have been reported to interact with nucleic acids, we investigated whether unr could bind to some classes of nucleic acids. We report here that unr has a high affinity for single-stranded DNA or RNA and a low affinity for double-stranded nucleic acids. Its low affinity for double-stranded DNA clearly distinguishes unr from the Y box factors. The binding of unr to RNA does not appear to depend upon extended sequence motifs but requires some level of sequence complexity as unr has only a low affinity for most simple polymers including polyA stretches. unr is also characterized by its low affinity for double-stranded and structured RNAs. We further determined that unr is mostly localized in the cytoplasm, and is in part associated with the endoplasmic reticulum. These studies indicate that unr is a novel single-stranded nucleic acid binding protein which is likely to be associated with cytoplasmic mRNA in vivo.

Cloning, Molecular↗
PubMed1994

Anti-tumor necrosis factor modulates anti-CD3-triggered T cell cytokine gene expression in vivo.

De novo expression of TNF, IFN gamma, IL-3, IL-4, and IL-6 genes was initiated rapidly by treatment of mice with anti-CD3. A specific feature of this reaction was that TNF was derived exclusively from T cells. TNF was produced both as a mature soluble trimeric protein and as a 26-kD anti-TNF-reactive protein compatible with membrane-anchored TNF. Pretreatment with anti-TNF did not affect anti-CD3-triggered TNF mRNA expression in T cells. In contrast, in vivo and in vitro anti-TNF treatment upregulated anti-CD3-induced IFN gamma mRNA expression and inhibited IL-4 mRNA expression. These latter effects were not dependent on TNF neutralization: pretreatment with soluble recombinant 55-kD TNF receptor (TBPI) as an alternative TNF-neutralizing agent did not modify the anti-CD3-induced cytokine profile. These results suggest that a direct interaction between anti-TNF and T cell membrane-anchored TNF could account for the observed modulation of cytokine gene expression. The increased expression of INF gamma mRNA observed in anti-TNF-treated animals correlated with a decrease in IL-3 and IL-6 mRNA expression. Conversely, IFN gamma blockade by a neutralizing anti-IFN gamma mAb led to a substantial increase in both IL-3 and IL-6 gene expression induced by anti-CD3. Taken together, these results strongly argue for the existence, in the anti-CD3-induced cytokine cascade, of IFN gamma-dependent regulation of IL-3 production, which in turn modulates IL-6 production.

Animals↗
PubMed1994

Infection with a Kirsten-retrovirus can induce a multiplicity of tumorigenic phenotypes in the interleukin-3-dependent FDC-P1 cells.

The identification of ras oncogenes in both human and animal tumors as well as in preleukemic and precancerous lesions suggests that activated ras genes participate in neoplastic development, yet the precise role of ras oncogenes in leukemogenesis is not clear. To assess the functional role of ras genes in tumorigenesis, we introduced with a retroviral vector either a wild-type (Gly-12) or a mutant (Val-12) Kirsten ras cDNA into the cells of a factor-dependent myeloid cell line, FDC-P1. FDC-P1 cells are nontumorigenic and their proliferation is dependent on either interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). The Ki-Val 12-infected FDC-P1 cell population is still strictly IL-3-dependent but has acquired the ability to survive up to 72 hours in the absence of growth factor and to form tumors in nude mice. These tumors are easily established into cell lines that are clonal and show a multiplicity of phenotypes with respect to their growth factor dependence. These results suggest that, in contrast with the overexpression of a normal Ki-ras, Ki-ras oncogene can efficiently promote the tumorigenic conversion of FDC-P1 cells. However, the clonality of the tumors as well as the distinct phenotypes indicates that other genetic events are required for tumorigenicity. Therefore, in FDC-P1 cells, an activated ras gene acts as a dominant oncogene through the induction of tumor progression. Finally, in this simple experimental system we observed a multiplicity of tumorigenic phenotypes which are reminiscent of those observed in patients with acute myeloid leukemia.

Animals↗
PubMed1993

Exon skipping in the expression of the gene immediately upstream of N-ras (unr/NRU).

The unr (or NRU) gene was identified during investigations of the structure of the N-ras locus in the genome of mammals. A striking feature of the unr/N-ras gene tandem is the short intergenic distance of 150 nucleotides which suggests the possibility of transcriptional interactions between the two genes. At present, the function of the unr gene is unknown, but the predicted translation product shows a distant relationship to a class of DNA binding proteins. Comparison of the two published cDNA sequences, from a human lymphocytic and a rat testis cDNA library, reveals a difference of 31 amino acids in the size of the predicted proteins. We show that this is due to the skipping of exon 5 within the human NRU gene and that a similar phenomenon occurs in the rat unr gene. Exon skipping takes place in all the cells and tissues we have analyzed and generates the predominant form of message, except in the brain where both classes are about as abundant. This exon skipping is independent of other aspects of unr expression such as the choice of the polyadenylation site.

Amino Acid Sequence↗
PubMed1993

In vivo cooperation between introns during pre-mRNA processing.

In higher eukaryotes the large number of introns present in most genes implies that the pre-mRNA processing machinery should be efficient and accurate. Although this could be achieved at the level of each intron, an attractive alternative would be that interactions between introns improve the performance of this machinery. In this study we tested this hypothesis by comparing the processing of transcripts of the tumor necrosis factor beta gene, which differ only by their number of introns. We took advantage of the ordered splicing of the three introns present in this gene to design constructs that should generate, as primary transcripts, molecules that are normally produced by splicing. We established that the apparent splicing rate of intron 3 is increased 2.5- and 3.5-fold by the presence of one or two other introns on the primary transcript, respectively. Similarly, the apparent splicing rate of intron 2 is increased by the presence of intron 1. As these effects involve the splice sites of the upstream intron, these observations support the existence of cooperative interactions between introns during pre-mRNA processing.

3T3 Cells↗
PubMed1992

Organization of the unr/N-ras locus: characterization of the promoter region of the human unr gene.

Investigations of the structure and expression of the N-ras gene in mammals has led to the identification of another gene designated unr, which is located immediately upstream of N-ras. These two genes are transcribed in the same orientation and the intergenic distance is of the order of 150 nucleotides. This genetic organization has been observed in the genome of guinea pig, rat, mouse and man with a very high level of sequence conservation in the intergenic region. This unusual gene clustering suggests that the transcriptional regulation of this locus could involve common regulatory sequences as well as transcriptional interference between the two genes. In this study, we have isolated and characterized the human unr promoter. A cluster of transcription initiation sites was mapped by primer extension and RNase protection and shown to be located in a CpG island devoid of TATA and CAAT boxes. Functional organization of the promoter was investigated by measuring the ability of a set of 5' deletions within a1 kb promoter region to drive the expression of the luciferase gene. These studies indicated a very strong promoter activity in NIH 3T3 cells and the presence of positive and negative regulatory domains. Nevertheless, a 90 bp fragment showed the same level of promoter activity as the 1 kb fragment. We also showed that ras genes can transactivate the unr promoter activity and that the 90 bp fragment responded to this transactivation.

3T3 Cells↗
PubMed1992

Inactivation of the murine N-ras gene by gene targeting.

The mammalian ras genes have been implicated in the genesis of a wide variety of tumors. Although it is likely that they play an essential role in signal transduction, their specific function is still unknown. To initiate a genetic analysis of the ras genes in mammals we inactivated the N-ras gene in murine embryonic stem cells by gene targeting. The frequency of integration at the N-ras locus of our targeting vector being low (of the order of 1/5000 transfectants), we used a positive/negative selection followed by an analysis of individual colonies in order to minimize the in vitro manipulation of the embryonic stem cells. Using this approach, we isolated two clones of ES cells with one inactivated N-ras allele. These cells have no distinctive phenotype either in vitro or in vivo in chimeric mice.

Alleles↗
PubMed1991

Influence of myc overexpression on the phenotypic properties of Chinese hamster lung cells resistant to antitumor agents.

In the Chinese hamster lung fibroblast cell line DC-3F, the development of resistance to different drugs, through several mechanisms like MDR expression or alteration of the DNA topoisomerase II activity, has been shown to be associated with a decreased tumorigenicity. Multiple studies have shown that the myc oncogene, in cooperation with ras, plays a major role in the oncogenic transformation of fibroblasts. As an approach to a better understanding of the relationship between the different phenotypic traits, we analyzed the expression of myc and ras oncogenes in the drug-sensitive DC-3F cells and in variants resistant to 9-hydroxyellipticine (9-OH-E) (DNA topoisomerase II alteration) or to actinomycin D (AD) (multidrug (MDR) expression). Southern and Northern blot analyses revealed about a 10-fold amplification and a 20-fold overexpression of the c-myc gene in the DC-3F cells as compared to the normal lung fibroblasts. Both amplification and overexpression are markedly decreased in the two resistant variants, ras gene copy number and expression were found to be identical in all cell types. In order to analyze the contribution of the decreased myc expression on the different phenotypic traits, the DC-3F/9-OH-E cells were transfected with the plasmid pSV-c-myc, and six clones expressing high amounts of the transfected myc were isolated and characterized. Morphological and caryological alterations, as well as an increased cloning efficiency in soft agar, indicated that the myc gene product was made in these cells. However, the tumorigenicity of the sensitive parental cells was not restored, thus showing that the decreased myc expression alone does not account for the loss of tumorigenicity in the resistant cells. 9-OH-E resistance was not modified in the transfected cells, while the cross-resistance of these cells to MDR-sensitive drugs, such as vincristine, actinomycin D, and taxol, was reversed roughly in proportion of the expression of the transfected myc.

Animals↗
PubMed1991

Stimulation of methotrexate resistance and dihydrofolate reductase gene amplification by c-myc.

We have hypothesized that the c-myc oncogene might promote DNA amplification. Resistance to methotrexate (MTX), a widely used cancer chemotherapeutic agent, often results from amplification of the gene coding for the target enzyme, dihydrofolate reductase (DHFR). We report here that gratuitously induced expression of c-myc in rat fibroblasts grown in the presence of MTX greatly increases the number of colonies resistant to the drug. This effect is not related to an alteration of cell growth, and it can also be observed to a lesser extent when c-myc is induced prior to selection in MTX. The DHFR gene is amplified in nearly half of the colonies cultured under selection conditions. Given the likely role of the c-myc product in DNA replication, these results strongly suggest that expression of c-myc plays a role in methotrexate resistance by promoting DNA amplification.

Animals↗
PubMed1991

Organization of the human N-ras locus: characterization of a gene located immediately upstream of N-ras.

The mammalian ras genes have been implicated in a wide variety of natural and experimental tumors. They code for small GTP binding proteins which are believed to play a central role in the control of cellular proliferation and differentiation. We have investigated the transcriptional organization of the human N-ras locus and characterized a transcription unit located immediately upstream of N-ras, which we designate by NRU for N-ras Upstream. NRU messages contain an open reading frame of 767 amino acids which shows no similarity with the ras proteins and provides no clue to the function of the corresponding protein. Of the order of 150 nucleotides separate the N-ras transcription initiation sites from the last NRU polyadenylation site and the same organization is present in the murine genome. Both genes are simultaneously expressed in all the cell lines and murine tissues we have analysed, and in all cases NRU messages accumulate to a higher level than those of N-ras. The small intergenic distance implies that, during transcription of NRU, RNA polymerases transcribe a substantial part of the N-ras gene, suggesting that this genetic organization participates in the regulation of N-ras expression.

Animals↗
PubMed1990

RNA processing is a limiting step for murine tumor necrosis factor beta expression in response to interleukin-2.

We have previously reported that tumor necrosis factor beta (TNF beta) expression is induced by interleukin-2 (IL-2) in the murine lymphocytic T-cell line CTLL-2. In this study, we have characterized the nuclear and cytoplasmic TNF beta transcript and assessed their role in TNF beta gene expression. A unique feature of TNF beta expression was the accumulation of nuclear precursors, which reflected a slow nuclear RNA processing. As a consequence, there was a delay in the appearance of cytoplasmic messengers after the transcriptional induction of TNF beta by IL-2. We also found that two messengers, the fully spliced messenger and an intron 3-retaining messenger, were exported to the cytoplasm and actively translated. The same pattern of expression was observed in concanavalin A-stimulated splenocytes, although the level of expression was much lower than in CTLL-2 cells. The simple genetic structure and the high level of accumulation of nuclear precursors make TNF beta a particularly attractive model system to use for studies of RNA processing and cytoplasmic transport of partially spliced messengers.

Amino Acid Sequence↗
PubMed1990

Mevalonate deprivation alters the induction of fos and myc by growth factors.

Besides cholesterol, mevalonate is the precursor of several isoprenoid compounds including the farnesyl moiety of isoprenylated proteins. Inhibition of mevalonate biosynthesis leads to a growth arrest that can be relieved by addition of mevalonate, but not of cholesterol. To get a better understanding of the mechanisms underlying this growth inhibition, we have investigated whether mevalonate derivatives are implicated in the early response to growth factors. Our results show that pretreatment of quiescent human fibroblasts with mevinolin, an HMG CoA reductase inhibitor, partially suppresses fos and myc mRNA accumulation in response to serum stimulation. This effect of mevalonate deprivation appears to be on the transcriptional regulation of fos and does not depend upon the nature of the initial events of signal transduction, since the same phenomenon was observed following EGF and TPA stimulation.

Blotting, Northern↗
PubMed1989

Mock retroviral infection alters the developmental potential of murine bone marrow stem cells.

Retroviral vectors were used to introduce an activated ras gene into murine pluripotent hemopoietic stem cells. We attempted to reconstitute the hemopoietic system of lethally irradiated mice with isolated spleen colonies obtained in vivo after injection of infected bone marrow cells. Spleen colonies derived from infected bone marrow were inefficient in promoting long-term survival of irradiated hosts. This loss of reconstitutive capacity of spleen colonies was not due to the retroviral infection per se but to the in vitro culture of spleen colony precursors. Incubation for 24 h in the presence of fetal calf serum and interleukin-3 without virus-producing cells was sufficient to abolish completely the reconstitutive capacity of spleen colonies while maintaining both self-renewal and pluripotential capacities of spleen colony precursors. These results show that the in vitro manipulation of stem cells that is included in current protocols for retroviral infection can modify the developmental potential of these cells. This finding clearly indicates that the use of retroviral vectors can introduce a bias in the analysis of hemopoiesis.

Animals↗
PubMed1989

c-Ha-ras transfection induces human immunodeficiency virus (HIV) transcription through the HIV-enhancer in human fibroblasts and astrocytes.

Transient transfection of ras expression vectors into human fibroblasts and astrocytes has been used to test the hypothesis that p21 ras, a known membrane signal transductor, may participate in pathways linking cellular activation and human immunodeficiency virus (HIV) reactivation. Expression vectors carrying the chloramphenicol acetyl transferase coding sequence under the control of various fragments of the long terminal repeat (LTR) of HIV were co-transfected with expression vectors of the mutated (val 12) c-Ha-ras gene or of its normal counterpart. Both forms of the ras gene induced transactivation of the HIV-LTR via the two direct repeat sequences which constitute the HIV enhancer. This repeat sequence was shown to be sufficient for ras-induced LTR transactivation. Other LTR sequences tested were not found to be responsive to co-transfected ras expression vectors. Deletion of the TAR sequence impaired the response to tat, but not to ras co-transfection. The mutated ras gene was more efficient than the proto-oncogene in activating the HIV enhancer. Transfection of ras was shown to enhance transcription of a complete provirus DNA clone of HIV-1. Such findings may shed new light on the mechanisms through which cell membrane activation signals result in HIV reactivation.

Astrocytes↗
PubMed1988

Regulation of pim and myb mRNA accumulation by interleukin 2 and interleukin 3 in murine hematopoietic cell lines.

We have studied the mRNA accumulation of pim and myb genes in two interleukin 2- (IL2-)dependent, CTLL-2 and B6.1, and one IL3-dependent, FDC-P2, murine hematopoietic cell lines. To be able to dissociate the IL2 response from the phenomenon of lymphocyte activation, we used cell lines constitutively expressing the high affinity IL2 receptor. Deprivation of IL2 for 16 h led to an accumulation of CTLL-2 cells in G0/G1, and stimulation with IL2 induced a progression in S phase after 10 h. An increased accumulation of pim mRNA was observed in all cases in response to IL2 or IL3. This regulation did not require de novo protein synthesis and was, in CTLL-2 cells, mostly at the transcriptional level. Expression of myb was more complex: in CTLL-2 and FDC-P2 it is high and constitutive, while in B6.1 it is low and induced by IL2. This difference in myb regulation correlates with the higher level of myb expression in immature cells, as only B6.1 is functionally mature. Furthermore, it shows that transcription of myb does not affect the control of the cell cycle by the growth factors IL2 and IL3. These studies demonstrate that pim belongs to the small group of protooncogenes that can be induced during the primary response to growth factors (fos, myc, and myb) and that constitutive expression of myb, at least at the RNA level, is not sufficient to abrogate the growth factor requirement of hematopoietic cell lines.

Animals↗